It is a Powerunit DC/AC 250 watts No.1 (American)(1A),Model DB-12-A,Pincor specification No. SS-2856 1942.I believe that the actual engine is a Briggs and Stratton ( no idea of the model), and that the unit was used in WW2 to power wireless sets.

If anyone knows anything about these units then please let me know.Thank you.

Hi Hamish,Thanks for your reply - I thought that as the engine is American 'Stak would be the place to access information,but as you say the trail has gone cold.I did contact the person you mentioned and he is looking to see if he still has a manual.All the best,Kev.